Posted
by
kdawsonon Tuesday February 19, 2008 @08:35PM
from the here-there-be-winps dept.

ethericalzen writes "A BBC article highlights a theory that the first stars may have been powered by dark matter. A group of US scientists published a paper in Physical Review Letters speculating that, unlike the stars of today, which are powered by nuclear fusion, early stars might have been powered by the abundant dark matter crowding the universe after the Big Bang. The theory suggests that these stars would have collided and destroyed one another before nuclear fusion had a chance take hold." The BBC perhaps overstates the certainty with which the dark-matter theory is held, and doesn't mention that the postulated properties of such particles are completely speculative.

First off, dark matter isn't dark but transparent. Then, how could say methane and oxygen which are transparent create light when burning together? Oh I know! Maybe that's because it's not the matter that releases light/energy but its transformation.

How do you overstate the certainty of dark matter? Last I read, the only serious alternatives were that there's more interstellar dust than we thought (improbable considering the observations of the bending of light), modifications to the theory of gravity (few supporters, unlikely, especially with said observations), and string theory.

Outside of string theory and MOND, what is there that's a serious contender? There are fringe theories, and they could be correct, but that doesn't change the fact that there's a lot of certainty out there for dark matter.

Of course... but then there's at least as much certainty that there's a heck of a lot about the universe we don't know anyways... in other words, it's actually a rather useless theory, except to the extent that I suppose it makes scientists feel better because it makes their existing theories still work without being forced to confront the possibility that we really don't have a clue about anything.

How about: "These particular results of the use of Math do not really make sense, and we cannot really verify/falsify them. It's fun, but right now I have to do some shopping, so I'll go build a bridge or do something for which I can get paid, and with the money I get I'll buy that second-hand Cray you saw yesterday and we'll be back in the business of discovering particles that are so small that, if Heisenberg was right, we can't know much about them but a product of their speed and of their mass, or bac

"makes their existing theories still work without being forced to confront the possibility that we really don't have a clue about anything."Most of the theory right now revolves around our solar system and what occurs there. We have a whole set of formulas to calculate it.

But those formulas fall apart when applied to the very small such as an atom so we make exceptions.

Each planet rotates a given speed based upon its distance from the sun, yet electrons do not follow that same calculation around the proton.

Each planet rotates a given speed based upon its distance from the sun, yet electrons do not follow that same calculation around the proton.

And that, of course, is for a very good reason: the electrons aren't in orbit around the nucleus in the same way that the Earth is in orbit around the Sun. If they were, electro-magnetic attraction would pull them into direct contact almost instantly.

I think he was alluding to the fact that there is a new fundamental force in action that makes gravity insignificant at those scales. In other words, why are we so certain dark matter is responsible, and not some fundamental force such as the MOND premise.

MOND isn't a serious contender because it still requires dark matter. So if you don't like the AMOUNT of dark matter, you might favour MOND. If you don't like dark matter at all, then it's not going to save you.

Actually, it seems to me that the universe expanding completely uniformly in higher dimensions than what is visible would still explain all of the non-uniform expansion that dark matter was apparently invented to explain. It baffles me as to why they would invent the notion of something invisible to explain anomalous observations instead of going with a no less workable and radically simpler theory.

Actually, it seems to me that the universe expanding completely uniformly in higher dimensions than what is visible would still explain all of the non-uniform expansion that dark matter was apparently invented to explain. It baffles me as to why they would invent the notion of something invisible to explain anomalous observations instead of going with a no less workable and radically simpler theory.

So far as I know, only time is sufficiently convolved with our "regular" three spatial dimensions so as to be considered another (via Lorentz transforms). Higher dimensionality is invoked all the -- ahem -- time, but these are generally things like Hilbert spaces, of infinite dimensionality.Hyperspace coordinates are eminently helpful in, e.g., nuclear theory, but there are mappings from these to 4-space, and I am unaware if anyone thinks that the transformations are merely convenient ways to separate out e

Just the time dimension. You're proposing extra spatial dimensins, which is not something that "we had already accepted". String theorists like extra dimensions, but there's no evidence of them, and string theorists aren't the whole physics community. Plus, not even string theorists have managed to do what you insist is "radically simple": produce a dark matter equivalent using only the structure of higher-dimensional spacetime. Believe me, if string theory had a simple, workable alternative to dark ma

Actually, it seems to me that the universe expanding completely uniformly in higher dimensions than what is visible would still explain all of the non-uniform expansion that dark matter was apparently invented to explain. It baffles me as to why they would invent the notion of something invisible to explain anomalous observations instead of going with a no less workable and radically simpler theory.

How do you test for "the universe expanding completely uniformly in higher dimensions"?

The fairy Tinkerbell wafting around and sprinkling pixie dust to make everyone unhappy and thus magically heavier is another "working theory". It's when you have a testable hypothesis and the test agrees with your theory that you have something you can prove or disprove.
Dark Energy has about as much experimental proof as the Tinkerbell theory I just mentioned. It solves some mathematical models based on rather scant data, but lacks experimental or other observational foundation.

You have no idea how good it feels to see that I'm not the only one who suspects that Dark Matter and Dark Energy are just ad hoc inventions to make an old theory explain new facts. Personally, I think that when we understand what's happening, we'll find no need for either.

I think you are getting mixed up between dark matter and dark energy.Dark energy has been invented to explain why the expansion of the Universe is speeding up.Dark matter is to explain why galaxies stay together without having enough observable mass.

Actually, it seems to me that the universe expanding completely uniformly in higher dimensions than what is visible would still explain all of the non-uniform expansion that dark matter was apparently invented to explain.

We don't really observe non-uniform expansion... we do see random inhomogeneities left over in the current distribution of cosmic background radiation and galaxies, thought to be partly due to inflation and partly to dark matter.

Or perhaps subtle flaws in the local measurements which are so wildly extrapolated into asumptions about the size of the universe, its age, its distribution of galaxies, etc.? We just saw, here on Slashdot, an announcement that commonly available data show the thickness of the Milky Way is twice the published value. When you extrapolate the limited astonomical data we have, all the way out to the edges of the universe and our ability to measure, you can't take the numbers too seriously and try to make too m

Other alternatives being explored generally rely on alternatives to General Relativity (for instance, TeVeS) to describe results that are attributed to dark matter.
I was actually at a day of seminars at the Perimeter Institute last fall where Katherine Freese gave a talk on this subject. The next speaker was actually talking about alternatives to GR and offered an interesting analogy. Early on, when astronomers were still mapping out the solar system, they noticed that Uranus' orbit did not conform to what was predicted by Newtonian gravity. As a result, they predicted a 'dark' body farther out who's orbit was influencing Uranus. This turned out to be Neptune. On the other hand, the precession of the perihelion of Mercury, which was also believed initially to have been caused by an unseen planet (which they called Vulcan), was found to be the result of the failure of Newtonian gravity, and is now seen as confirmation of General Relativity. He concluded that both avenues of enquiry are valid and should both be followed.

Another analogy for dark matter is the neutrino: it was an invisible, virtually non-interacting particle introduced purely to maintain the internal consistency of the known laws of physics (the conservation laws). It was 12 years before they were actually discovered, since they interact so weakly. Dark matter also interacts weakly, but is thought to be much more massive than a neutrino, so it's difficult to produce in a particle accelerator.

for the fact that MOND gives good results.There is nothing wrong with Dark Matter(DM) as a concept. It is certainly possible that DM exists. The only problem with DM (at least at the Galactic scale) is that MOND gives very good results. Its like the Max Planck's corpuscular theory of Black Body Radiation. Planck assumed that radiation could only have some allowed energy levels. This assumption was able to fit the Black Body Radiation curve very well. This is how Quantum theory was born.

There is the difficulty that we've now directly observed the gravitational effects of blobs of "dark matter" which became separated from their host galaxies. MOND or not, we need to account for what that stuff is somehow.

But MOND doesn't give good results, except for galactic rotation curves, which are by far not the only evidence for dark matter.

DM at galactic scale would be perfectly fine if we did not have MOND work so well.

DM at galactic scale is still perfectly fine, regardless of the existence of MOND or any other theory. Whether theory Y also explains observations has nothing to do with how well theory X explains those observations. (Well, unless you propose they're both true, instead of being competing.)

If all we had were galactic rotation curves, then DM and MOND would both be fine. Of cour

I did not say that MOND requires curved space. Just that it could explain MOND. Mass curves space-time and this curvature exerts a force, we know as gravitational force. If the space-time that makes up universe is itself curved say because of the expansion, then that curvature will itself create a force. Which will manifest itself as a force occurring without any matter. This force will tend to force objects into rotational motion. The force will be negligible near large masses, as the gravitational force w

I did not say that MOND requires curved space. Just that it could explain MOND.

There are curved spacetime theories of MOND, but their existence does not follow from what you say below.

Mass curves space-time and this curvature exerts a force, we know as gravitational force. If the space-time that makes up universe is itself curved say because of the expansion, then that curvature will itself create a force. Which will manifest itself as a force occurring without any matter.

Not necessarily. Take general relativity without a cosmological constant. It admits curved, expanding spacetimes, but it can't replace dark matter. You have to make more radical changes to the dynamics of spacetime to do that. (In TeVeS theory, you need to have extra scalar and vector fields in addition to the usual tensor field of gravity.)

How do you overstate the certainty of dark matter? Last I read, the only serious alternatives were that there's more interstellar dust than we thought (improbable considering the observations of the bending of light), modifications to the theory of gravity (few supporters, unlikely, especially with said observations), and string theory.

I think kdawson meant that they were overstating the certainty of this theory, not the existence of dark matter in general. To be honest, I'm not sure why there are so many people (at least on/.) who want to relegate dark matter the the mathematical physics bin along with string theory. There's plenty of evidence for it. We've even observed gravitational lensing from dark matter. Dark energy [wikipedia.org] on the other hand, may be something of a luminiferous aether [wikipedia.org].

Out of curiosity, is the radiation-to-normal-matter ratio about the same as the supposed dark-energy-to-dark-matter ratio? If it is, wouldn't the simplest explanation of dark energy be that it's the equivalent of light for dark matter?

Considering that the need for Dark Energy to explain the expansion of the universe is in question [slashdot.org], I don't know. We know very little about Dark Matter and Dark Energy. Now we hear that our own galaxy might be twice as thick [usyd.edu.au] as we previously thought. Dark Energy and Dark Matter are added to observed data to come up with models [wikipedia.org] to explain observations. I'm thinking if 75% of the energy in the model is no longer required to explain observations and the 4% of free hydrogen and helium might be doubled that m

IANAP, but our understanding of gravity isn't complete. We have a fairly good understanding of how it operates, but we're not sure what it even is. We assume the effects of gravity remain the same throughout the universe, and throughout time. We assume it works on very large scales much like it does on smaller scales. We have no idea how it works on quantum scales.

With all these uncertainties I think it's jumping the gun to assume any gravitational effects we can't explain with our models of the univers

Of course, if you just re-solve the General Relativity equations using the data that's been collected in the last 100 years, it appears that dark matter may be completely unnecessary. This was previously discussed here [slashdot.org].

The BBC perhaps overstates the certainty with which the dark-matter theory is held, and doesn't mention that the postulated properties of such particles are completely speculative.

Aside from the actual topic, I want to say that I was pleasantly surprised to see the summary correcting for the improper journalism of the article. Overzealous interpretation of scientific results by journalists is a common complaint around here, and our editors who know that (and can easily recognize it when they review the submission) are the perfect ones to catch the inaccuracy and notify us in advance, so we aren't mislead about the actual claims of the scientific paper. Thanks, kdawson, for the excellent editorial addition to this story.

everything is explained by dark matter. Universe heavier then we think it should be? dark matter. can't figure out the big bang? dark matter. I bet soon enought someone will figure out a way to tie dark matter to the cables in the middle east that got cut the other day.

So if I understand all this, it would appear that dark matter came out of grey matter.

I had this idea that if you take the early universe, place it in a top loading washer and set the dial to spin, then press start, wouldn't you get accelerating expansion? I just Googled this an apparently it's an old idea. Of course, you need a extra-dimensional washer but I'll leave string/brane theory to explain all this. Fits in well with bubble/suds universes too.

That's not accurate, there is much evidence supporting the idea of massive particles which do not interact via the electromagnetic, strong, or weak forces. There is, for instance, the observation of lensing in the Bullet Cluster [nasa.gov] last year which put to rest many of the modified gravity theories. There is also the recent observation reported earlier on/. [slashdot.org] of a galaxy composed of stars whose motion can be described without dark matter. The latter observation is particularly damning, if the effect were due to a misunderstanding on our part of the gravitational force or some quantum mechanical property of normal matter then it should be seen everywhere.

There is zero evidence of Dark Matter. Circumstantial but it's just like string theory: a lot of take, no proof.

There's as much evidence for dark matter as there is for black holes or neutron stars or anything else in cosmology that we can't actually visit.

Dark Matter was just one hypothesis among many for why galaxy rotation wasn't as expected until we started getting the very precise measurements of the cosmic microwave background radiation a couple of years ago. That made it clear that the matter mass of the early universe was about 80% non-baryonic, reacting to gravity but not light pressure. The percentage and distribution was predicted well by a dark matter theory, and it has explained some later observations as well.

Ah, I see I missed the part in the article saying fusion reactions would maybe not start. Hmm, yes then, I also think it would be borderline to actually call them stars? After all, brown dwarves are called "failed" stars, because they never get the fusion reactions going due to too low mass.

Ok. If we were a simulation, and were simulating only the important stuff, that simulation would include the appearance of particles far off in the light-cone. To our PoV, it'd be as if they were actually always simulated.

The irony of this of course is that the universe could really be only 6000 years old or whatever under this model. I mean, when you play an RPG and you read some book in the game referring to a battle that took place 500 years prior, that doesn't mean that the game is 500 years old...

For all you know the universe was created this morning and you just think you remember everything prior.

I find this thought interesting because it is similar to an analogy I came up with recently. Rather than thinking of dark matter as unrendered parts of a scene, think of it like this: If the physical world were to be equated to an LCD monitor, then dark matter would be the electrical charges symbolizing bits of data coursing through the cpu and circuitry. Hence, the physical world is only a window into the underlying "dark matter program". Or, in a similar analogy, the physical world would be equated to

The proposed idea that early stars were made of dark matter, etc. is pure speculation. Speculation is NOT a theory. Let's review: scientifically speaking "a theory is a systematic and formalized expression of all previous observations, and is predictive, logical, and testable" [wikipedia]. A theory also is built on a substantial mathematical/physical/chemical foundation on which it rests. Unfortunately there is an air-headed defintion that 'theory' is a speculative conjecture, opinion, or untestable n

How weakly do Weakly Interacting Massive Particles interact? Now we have them colliding and annihilating themselves? Often enough to create enough pressure to offset the gravity trying to pull the "star" together? Just how wimpy are your WIMPs?

And I also am not convinced these hypothetical objects should be called "stars." Quark stars and neutron stars were at least formerly fusion-powered stars before losing their morals and becoming degenerate matter.

Eventually this will begin to show that the "Big Bang" did not start it all to begin.As the astronomers equipment gets better, so it will be that science will have to change the reasons behind what it is seeing. Look for postulates of dark energy/matter (multidimensional areas in space), and also postulates of light changing its speed from place to place, depending upon the formula around localized reality, especially the time frame.

Not that it really matters, because our perceptions will also be different in those places:P I suppose if the frames are localised then that's one way of being able to measure the differences though, rather than just theorising.. possibly by sending an atomic clock in, retrieve it, and see how much difference in time had elapsed? Though if the journey is long then the speed at which the clock is moving would also change how fast it 'ticks', or warp time around it, whatever you want to say. Or is there a mo